Geoscience Reference
In-Depth Information
FIG
38.
Typical Devonian sedimentary basin in the Southwest Region.
FIG
39.
The major bedrock structures of Southwest England and South Wales.
Another feature of the mountain building is that muddy material - the most
abundant sediment in the Southwest Region - was often converted into slates that can
typically be split into thin sheets and are said to possess a 'slatey cleavage'. These
rocks are locally referred to as
killas
, to distinguish them from other rocks with no
cleavage, particularly the granites. The conversion into slates took place during the
folding and fracturing of the mountain building, when the original muds, rich in clay
minerals, were buried deeply below other sediments and then compressed to produce a
new layering (or
cleavage
).
